CVE-2025-68366 nbd: defer config unlock in nbd_genl_connect
A use-after-free in the Linux kernel NBD driver allows local attackers to cause a crash or potentially escalate privileges via race conditions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-68366?
CVE-2025-68366 is an use after free vulnerability in Linux, published on 24 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
nbd: defer config unlock in nbd_genl_connect
There is one use-after-free warning when running NBD_CMD_CONNECT and NBD_CLEAR_SOCK:
nbd_genl_connect nbd_alloc_and_init_config // config_refs=1 nbd_start_device // config_refs=2 set NBD_RT_HAS_CONFIG_REF open nbd // config_refs=3 recv_work done // config_refs=2 NBD_CLEAR_SOCK // config_refs=1 close nbd // config_refs=0 refcount_inc -> uaf
------------[ cut here ]------------ refcount_t: addition on 0; use-after-free. WARNING: CPU: 24 PID: 1014 at lib/refcount.c:25 refcount_warn_saturate+0x12e/0x290 nbd_genl_connect+0x16d0/0x1ab0 genl_family_rcv_msg_doit+0x1f3/0x310 genl_rcv_msg+0x44a/0x790
The issue can be easily reproduced by adding a small delay before refcount_inc(&nbd->config_refs) in nbd_genl_connect():
mutex_unlock(&nbd->config_lock); if (!ret) { set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags); + printk("before sleep\n"); + mdelay(5 * 1000); + printk("after sleep\n"); refcount_inc(&nbd->config_refs); nbd_connect_reply(info, nbd->index); }
Which versions are affected by CVE-2025-68366?
How do I fix CVE-2025-68366?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-68366 being exploited?
There is no known exploitation of CVE-2025-68366 in the wild and no public exploit code.
Sources
Also known as AZL-73081, BELL-CVE-2025-68366, DEBIAN-CVE-2025-68366, GHSA-9x47-h3pc-w4pg, ROOT-OS-DEBIAN-11-CVE-2025-68366, ROOT-OS-DEBIAN-12-CVE-2025-68366 and 3 more.